In pursuing the long term objective of characterizing ionizing radiation damage in RNA and DNA the proposed research program will concentrate on two important areas. The first area is one in which information is clearly lacking and, from a biological standpoint, clearly needed. It is the determination of structural alterations in the sugar and phosphate moieties. The second area consists of extending current information on the radiation chemistry of nucleic acid constituents to systems which will answer how, when the constituent is incorporated into the native polymer, its radiation chemistry is altered. Each chemical system under study in this research program reflects these two areas of work. The chemical systems to be studied include: (1) mononucleotides, where characterization of damage to the sugar and phosphate moiety will be emphasized, (2) dinucleotides and other organic phosphodiesters, where attention will be focused on the phosphodiester moiety, (3) pyrimidine and purine base pairs, where the effects of hydrogen bonding and base stacking on radiation damage is to be ascertained. The method of procedure will center on characterizing free radical events using electron spin resonance. Irradiated chemicals will be studied by electron spin resonance in the form of single crystals, powders, and frozen solutions. Where feasible non-radical products, predicted from free radical precursors, will be studied using other spectroscopic and chromatographic techniques.